I've added a simple ICL7667CPA MOSFET-driver to the GPIO of the
Raspberry. It's power supply is 5V coming from the GPIO itselfe. This
leads to a 5V rectangular signal with lower output impedance. I've
coupled the output matching circuit so that the output power is now 50
mW / 17 dBm, i.e. 7 dB more power then in my previous test.
Iamge:
https://dl.dropboxusercontent.com/u/19882028/MF/17dBm%20RPI%20WSPR.jpg

The beacon is running now on 475.685 kHz.

73, Stefan/DK7FC

Am 18.03.2015 21:45, schrieb DK7FC:

Hi MF,

Today i've got i 3rd Raspberry Pi. I quickly installed the WSPR
softaware and since a few minutes i am transmitting WSPR-2 on 630m, my
usual frequency 475.685 kHz.

I'm directly using the GPIO output pin, without an amp stage behind!
The rectangular 3.3V output voltage is passing a cap and an isolation
transformer (FT50-77) as well as a simple pi-filter, because it is a
Raspberry pi! ;-)

I measured an output power of about 10 mW at 50 Ohm. It is now
connected to my MF antenna and transmits in a 100% duty cycle. I still
have to learn how to reduce it but this will not take long.

With 10 mW TX power i managed decodes by 3 stations now.
3 spots:

Timestamp

Call

MHz

SNR

Drift

Grid

Pwr

Reporter

RGrid

km

az

2015-03-18 20:32

DK7FC

0.475684

-21

0

JN49ik

0.01

DH5RAE

JN68qv

345

98

2015-03-18 20:12

DK7FC

0.475685

-24

0

JN49ik

0.01

F1AFJ

JN06ht

667

247

2015-03-18 20:06

DK7FC

0.475683

-27

0

JN49ik

0.01

DL1DBC

JO41bi

217

349

Does someone have good ears to get a decode from me? :-) It is a
challenge! :-)

73, Stefan/DK7FC

PS: The signal is so weak that my RX antenna frontend is not
overloaded, so at that power level i can transmit and receive to the
same time :-)
PPS: A small amp stage will follow soon, i intend to use an BS170
running at 5 V.